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RESEARCH

Paris Covered in Smog

On Wednesday, December 7, 2016, the air quality monitoring organization Airparif announced the longest and most intense peak of winter pollution in the Paris region in more than 10 years. What is this pollution? How does it form? Sébastien Payan, professor-researcher in Atmospheres, Environments and Space Observation Laboratory (LATMOS: under the co-supervision of UPMC/CNRS/UVSQ), sheds some light on the subject.

Unlike the ozone pollution peak in Paris this summer, the smog (a thick brownish haze) currently observed in Île-de-France is due to the accumulation of fine particles. "They are aerosols, particles suspended in the air," explains Sébastien Payan. "In town, they are mainly produced by the combustion created by vehicles. Using wood for heating, certain industrial installations, or the application of fertilizers also play an important role in this phenomenon. The resurgence of these emissions, combined with anticyclonic conditions, favor the accumulation of fine particles. They are concentrated in a thin layer of stagnant air above the ground.”
A meteorological disturbance, such as rain or wind would make it possible to return to normal by dispersing this layer of aerosols. The particles would again get mixed with the air, or would be washed into the ground by the rain. The current cold weather also resulted in a greater than usual emission of wood-based particles. The production of pollutants is more condensed, hence more visible and detrimental to health. "Fine particles can cause serious respiratory problems by deeply nesting in the pulmonary alveoli." The emergency measures taken by police headquarters should make it possible to temporarily limit the combustion by reducing traffic by 50%. "However, only 5% of the most polluting vehicles account for 20% of car pollution. It should also be possible to qualify the type of vehicle," says Prof. Payan.